linux-kernel - Re: [RFC PATCH 3/3] iommu/vt-d: Show region type in arch_rmrr_sanity

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Message-ID: <20220704111529.6pdlueeu2beo64ha@ava.usersys.com>
Date:   Mon, 4 Jul 2022 12:15:29 +0100
From:   Aaron Tomlin <atomlin@...mlin.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Aaron Tomlin <atomlin@...hat.com>, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        joro@...tes.org, will@...nel.org, dwmw2@...radead.org,
        baolu.lu@...ux.intel.com, hpa@...or.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3] iommu/vt-d: Show region type in
 arch_rmrr_sanity_check()

On Mon 2022-07-04 11:39 +0100, Robin Murphy wrote:
> On 2022-06-11 21:48, Aaron Tomlin wrote:
> > This patch will attempt to describe the region type in the event
> > that a given RMRR entry is not within a reserved region.
> 
> Hmm, is this useful information for the user? You'd hope the firmware vendor
> knows the memory map already, but either way, is it particularly likely that
> anyone would be noticing and caring about this warning in a context where
> they couldn't just scroll further up the log and cross-reference the full
> memory map listing? If so, it might be worth clarifying what that use-case
> is, since as it stands there doesn't seem to be much justification for the
> "why" here.

Hi Robin,

Thanks for looking at this.

Honestly, the only justification for the modification/or proposed changes
is to have more insight when this statement is provided in total isolation
and the RAM map listing (as per e820__print_table()) is no longer available
to reference.

> > diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> > index 95b994cf80cd..165e9a444bb9 100644
> > --- a/arch/x86/kernel/e820.c
> > +++ b/arch/x86/kernel/e820.c
> > @@ -1073,7 +1073,7 @@ void __init e820__finish_early_params(void)
> >   const char *__init e820_type_to_string(struct e820_entry *entry)
> >   {
> > -	switch (entry->type) {
> > +	switch (entry && entry->type) {
> 
> Have you tested this for anything other than E820_TYPE_RAM? I think
> sufficiently up-to-date compilers should warn you here anyway.

I have not.


Kind regards,

-- 
Aaron Tomlin